Approximately 2.2 million bone grafting procedures are performed worldwide to repair musculoskeletal defects, with approximately 500,000 bone grafting procedures being performed in the U.S. alone. Such musculoskeletal defects often result in pain and limited mobility, and therefore significantly impact the quality of life of affected individuals.
Bone is one of the few adult tissues with the capacity for true self-healing. Unlike soft tissue injuries, which generally result in the formation of scar tissue, bone healing concludes with the actual regeneration and reconstitution of the injured tissue, including the biochemical and biomechanical properties.
The need for bone regeneration arises in cases of bone loss due to trauma, tumor resection, or disease. Traditional orthopedic practice relies on the ability of a surgeon to drill, cut, ream, and realign bone. The success of these procedures requires technical skill and well-designed hardware. In a majority of cases, this is sufficient for healing, due largely to the remarkable capacity of bone for self-regeneration. Certain fractures and bone defects, however, require additional bone augmentation. The current procedures for bone augmentation include autologous and allogenic bone grafting, and more recently, ceramic and composite substitutes for bone grafts.
The clinical gold standard for bone regeneration has been autologous bone grafting, as it provides osteogenic cells and osteoinductive factors for bone healing. Though autologous bone grafting has been successful in many cases, it has significant disadvantages including limited graft material and morbidity of the donor site. These limitations have led to increased use of allograft bone as a substitute for autologous bone. Allograft bone, however, is inferior to autologous bone due to its reduced biological activity after processing. In addition, allograft bone grafting is associated with a high rate of complications and late fractures as well as a risk of disease transmission. The high failure rate of allografts is largely attributable to the inability of the graft to revascularize and remodel. Ceramic and polymer based bone graft substitutes have recently been introduced and are being used frequently. But, ceramics tend to be brittle, and polymers suffer from limited bioactivity and strength and may need to be supplemented with osteogenic cells and growth factors.
Tissue engineering research has focused on therapeutic strategies for repairing bone defects by the delivery of biological agents along with biodegradable scaffolds. Both two- and three-dimensional scaffolds have been designed to provide a template for bone repair. Though the focus has been to create three-dimensional scaffolds having adequate strength to support in vivo loading, most scaffolds do not provide an optimal environment for cellular function, and suffer from slow resorption kinetics. Moreover, exogenous cells delivered at the center of these scaffolds in vivo may not survive due to the initial lack of vascularity at the defect. Thin, two-dimensional membranes have been used for bone repair by placing them along the periosteal surface to demarcate the osseous from the non-osseous region. Though this technique (called guided bone/tissue regeneration) has been highly successful in the dental field for bone regeneration, it has not been quantitatively evaluated for the load bearing case of long bone defects.
Accordingly, there is a need for improved bone grafting techniques that promote bone regeneration by facilitating cellular and vascular ingrowth into the defect space. It is to the provision of such improved systems and methods for regenerating bone that the various embodiments of the present invention are directed.